Utilizing material from spontaneous and inevitable abortions and their parents and from mentally retarded males we will determine: (1) the origin of the additional chromosome in trisomics, the additional haploid set in triploids and the mutation in structural aberrations by the use of chromosome heteromorphisms; (2) whether age-related somatic non-disjunction is correlated with meiotic non-disjunction as measured by the production of trisomic conceptuses; (3) the contribution of chromosome aberrations and ABO blood group incompatibility to fetal wastage and the practicality of using spontaneously aborted fetuses for population surveillance for mutagens and teratogens; (4) the cytogenetic status of trophoblast disease; (5) the relationship of race and social class to the epidemiology of trophoblast disease; (6) whether the source of the X-chromosome is related to its activation or inactivation and whether an active paternally derived X-chromosome in trophoblast plays any part in the genesis of trophoblast disease; (7) a method for enhancing the appearance of the abnormal X-chromosome in Renpenning's syndrome and the formal genetics and effect on retardation of the abnozmal chromosome and its frequency among mentally retarded males.